The present invention relates generally to ferrules for fiber optic connectors and associated fabrication methods and, more particularly, to ferrules designed to facilitate fiber-to-fiber contact once a pair of fiber optic connectors have been mated, as well as associated fabrication methods.
Optical fibers are being increasingly utilized for a variety of applications including data transmission and the like. In order to interconnect the optical fibers, the fiber optic connectors that are typically mounted upon the opposed end portions of the optical fibers are appropriately mated. While the optical connections established by the mating of a pair of fiber optic connectors is generally quite good, some modern applications are placing increased performance and reliability demands upon optical fiber networks. In this regard, the optical connections established by mating a pair of fiber optic connectors preferably have relatively low attenuation and a small return loss.
In order to decrease the attenuation and return loss introduced by a fiber optic connector, conventional fiber optic connectors are designed such that fiber-to-fiber contact is established between the optical fibers upon which the respective fiber optic connectors are mounted. For example, fiber-to-fiber contact is preferably established between each optical fiber of a first fiber optic cable upon which a first fiber optic connector is mounted and a respective optical fiber of a second fiber optic cable upon which a second fiber optic connector is mounted once the first and second fiber optic connectors have been mated.
Unfortunately, the front faces of the ferrules of most fiber optic connectors have angular errors and are therefore not completely perpendicular to the optical fiber axes of the end portions of the optical fibers upon which the ferrules are mounted. In addition, the front faces of the ferrules of most fiber optic connectors are not perfectly flat. As such, the end portions of the optical fibers that are flush with the front face of the ferrule of a conventional fiber optic connector may not establish fiber-to-fiber contact with the corresponding optical fibers of another fiber optic connector since some portions of the front face of the ferrules may actually protrude outwardly beyond the end portions of the optical fibers. By protruding outwardly beyond the end portions of the optical fibers, portions of the front faces of the ferrules may contact before the optical fibers make fiber-to-fiber contact, thereby effectively preventing fiber-to-fiber contact. Likewise, dirt or other particles that settle upon the front face of the ferrule may prevent fiber-to-fiber contact in instances in which the end portions of the optical fibers are flush with the front face.
In order to overcome these problems and to provide for fiber-to-fiber contact, notwithstanding angular errors and dirt accumulation, the end portions of the optical fibers upon which the ferrules are mounted generally protrude or extend slightly beyond the front face of the respective ferrule. In this regard, the end portions of the optical fibers generally protrude by between about 500 nanometers and about 1,000 nanometers beyond the front face of the respective ferrule. As such, fiber-to-fiber contact can be established even if the front face has angular errors or if dirt or other particles have accumulated upon the front face.
In order to mount a fiber optic connector such that the end portions of the optical fibers extend beyond the front face of the ferrule by a predetermined protusion distance, the optical fibers are typically inserted through and epoxied or otherwise secured within the optical fiber bores defined by the ferrule such that the end portions of the optical fibers extend beyond the front face of the ferrule by more than the desired protrusion distance. The end portions of the optical fibers are then polished until the end portions of the optical fibers protrude beyond the front face of the ferrule by the desired protrusion distance. Upon mating a pair of fiber optic connectors, the end portions of the optical fibers that protrude beyond the front faces of the respective ferrules will generally make fiber-to-fiber contact.
Unfortunately, the fiber-to-fiber contact established by the mating of a pair of conventional fiber optic connectors having protruding optical fibers imparts forces to the optical fibers that may exceed the sheer stress of the epoxy that otherwise secures the optical fibers within the optical fiber bores of the ferrule in some circumstances. If the forces exerted upon an optical fiber exceed the sheer stress of the epoxy, the optical fiber will generally be pushed back into the ferrule such that the end portion of the optical fiber is flush with the front face of the ferrule or recessed within the respective optical fiber bore relative to the front face of the ferrule.
The likelihood that the epoxy bond will be broken typically increases as the temperature rises. In this regard, most ferrules are formed of a thermoset material that expands to a much greater degree than the optical fibers in response to heating. As such, the fit of the optical fibers within the respective optical fiber bores is loosened as temperatures increase such that the optical fibers are even more likely to be pushed back into the respective optical fiber bores defined by the ferrule.
In instances in which the optical fibers are pushed back into the respective optical fiber bores defined by the ferrules, intermateability problems may arise if the respective fiber optic connector is subsequently mated with another fiber optic connector. For example, a fiber optic connector in which the optical fibers have been pushed back into the respective optical fiber bores defined by the ferrule may fail to establish fiber-to-fiber contact in instances in which the fiber optic connector is decoupled and then mated with another fiber optic connector. As such, the attenuation and return loss of the resulting optical connection would be greatly increased relative to optical connections having fiber-to-fiber contact.
A ferrule is therefore provided that facilitates fiber-to-fiber contact without requiring the end portions of the optical fibers to protrude beyond the front face of the ferrule. Accordingly, the ferrule reduces the forces that are placed upon the optical fibers and prevents the optical fibers from being pushed back into the respective optical fiber bores defined by the ferrule. As such, the ferrule of the present invention serves to maintain fiber-to-fiber contact even in instances in which the fiber optic connector is decoupled from an original fiber optic connector and remated with another fiber optic connector. By maintaining fiber-to-fiber contact, the ferrule of the present invention also serves to maintain the attenuation and return loss of the resulting optical connection at a relatively low level, as desired in many applications.
The ferrule of the present invention includes a ferrule body having opposed front and rear faces. The ferrule body also defines at least one optical fiber bore extending between the front and rear faces and adapted to receive an optical fiber. In addition, each optical fiber bore opens through a medial portion of the front face of the ferrule body. Advantageously, the medial portion of the front face through which the optical fiber bores open protrudes outwardly beyond at least some peripheral portions of the front face. Although the medial portion can protrude outwardly beyond at least some peripheral portions of the front face by different amounts, the medial portion of one advantageous embodiment protrudes outwardly by about 1-5 millimeters relative to at least some peripheral portions of the front face.
Since only the medial portion of the front face of the ferrule, and not the entire front face, will make contact as a pair of fiber optic connectors are mated, fiber-to-fiber contact can be established between the optical fibers even if the optical fibers are positioned such that end portions of the optical fibers are flush with, slightly protruding beyond or even slightly recessed relative to the front face of the ferrule. In this regard, any angular errors in the peripheral portions of the front face or any dust or other particles that accumulate on the peripheral portions of the front face will not interfere with the fiber-to-fiber contact since the peripheral portions of the front faces of the ferrules are recessed and never come into contact. Since the end portions of the optical fibers can be disposed flush with the front face of the ferrule, the ferrule body can serve to at least partially support the forces that would otherwise be imposed upon the optical fibers, thereby reducing the load placed upon the epoxy that bonds the optical fibers within the respective optical fiber bores.
In one embodiment, the front face defines a smoothly curved surface in which the medial portion of the front face protrudes outwardly beyond peripheral portions of the front face. As such, the optical fiber bores defined by the ferrule body of this embodiment open through the apex of the curved surface defined by the front face of the ferrule body. In addition to extending lengthwise between opposed front and rear faces, the ferrule body also extends laterally between opposed first and second sides. In this embodiment in which the front face defines a smoothly curved surface, the front face has a uniform size and shape at all points between the first and second sides when taken in cross-section in a lengthwise extending plane that is disposed parallel to the first and second sides. While the front face of the ferrule of this embodiment is uniformly sized and shaped, the smoothly curved front surface can take on various configurations. Typically, however, the smoothly curved front surface defines a circular arc and, in one embodiment, defines an interior angle of no more than 180xc2x0 and has a radius of 5 millimeters.
In another embodiment, the medial portion of the front face through which each optical fiber bore opens is a planar surface that protrudes outwardly beyond peripheral portions of the front face. Although the medial portion is a planar surface, the peripheral portions of the front face of the ferrule of this embodiment are curved surfaces that taper rearwardly from the planar medial portion of the front face. While the planar medial portion can have various shapes and sizes, the planar medial portion of the front face of the ferrule of one advantageous embodiment is elliptical in shape and is oriented such that the major axis of the elliptical medial portion extends through each optical fiber bore.
In addition to the opposed front and fear faces, the ferrule has opposed first and second minor sides and opposed first and second major sides. Typically, the first and second minor sides are the opposed first and second lateral sides, while the first and second major sides are the opposed top and bottom sides of the ferrule body. In the embodiment of the ferrule having a front face with a planar medial portion, the peripheral portions of the front face that extend rearwardly from the medial portion of the front face to the first and second major sides preferably define a different radius than the peripheral portions of the front face that extend rearwardly from the medial portion of the front face to the first and second minor sides. For example, the peripheral portions of the front face that extend from the medial portion of the front face to the first and second major sides generally define a smaller radius than the peripheral portions of the front face that extend from the medial portion of the front face to the first and second minor sides. In one advantageous embodiment, for example, the peripheral portions of the front face that extend from the medial portion of the front face to the first and second major sides define a radius of 5 millimeters, while the peripheral portions of the front face that extend from the medial portion of the front face to the first and second minor sides define a radius of 15 millimeters.
According to one aspect of the present invention, a method is also provided for fabricating a multifiber ferrule having a planar medial portion. In this regard, a ferrule body is formed that has opposed front and rear faces and that defines a plurality of optical fiber bores extending therebetween and opening through a medial portion of the front face. The ferrule body that is formed also has opposed first and second minor sides and opposed first and second major sides. Once the ferrule body has been formed, the front face of the ferrule body is polished to form a curved surface. In particular, the peripheral portions of the front face proximate the first and second major sides are polished so as to have a different radius than the peripheral portions of the front face proximate the first and second minor sides. Preferably, the front face of the ferrule body is polished to form the curved surface by disposing polishing medial on a rubber pad and thereafter bringing the front face of the ferrule body into contact with the polishing media backed by the rubber pad. As such, the peripheral portions of the front face proximate the first and second major sides to define a smaller radius than the peripheral portions of the front face proximate to the first and second minor sides. Once the curved surface has been formed, the medial portion of the front face of the ferrule body is again polished to form a planar region, typically having an elliptical shape, through which the plurality of optical fiber bores open.
According to one embodiment in which the ferrule is a multifiber ferrule, the portion of the front face of the ferrule body through which each optical fiber bore opens defines a ring surrounding the respective optical fiber bore. According to this embodiment, each ring protrudes outwardly, such as by at least 1 millimeter, beyond other portions of the front face of the ferrule body. By protruding somewhat beyond other portions of the front face of the ferrule body, the rings also serve to prevent angular errors in the front face and dirt accumulation on the front face from interfering with the desired fiber-to-fiber contact. As such, the end portions of the optical fibers can be positioned flush with the rings while still permitting fiber-to-fiber contact. The rings can therefore support the forces otherwise imparted upon the optical fibers in order to reduce the load placed upon the epoxy bonding the optical fibers within the optical fiber bores.
In one embodiment, at least some of the rings intersect to form a series of interconnected rings that protrude outwardly beyond other portions of the front face of the ferrule body. In addition, the ferrule body of this embodiment generally defines a plurality of linearly aligned optical fiber bores including a pair of outermost optical fiber bores and at least one inner optical fiber bore. In order to provide additional support for the outermost optical fibers that typically make the initial fiber-to-fiber contact and, as a result, are generally subjected to greater forces than the remainder of the optical fibers, the rings that surround the outermost optical fiber bores can be larger in diameter than the rings that surround the respective inner optical fiber bores. For example, the rings that surround each optical fiber bore generally can have an inner diameter of 125 microns, with the rings that surround the inner optical fiber bores typically having an outer diameter of 250 microns and the rings that surround the outermost optical fiber bores having an even larger outer diameter.
By supporting the optical fibers and reducing the load on the epoxy bond between the optical fibers and the ferrule body, the ferrule of the present invention reduces the instances in which the optical fibers are pushed into the respective optical fiber bores. As a result, fiber optic connectors that include the ferrules of the present invention can be repeatedly remated in a manner that establishes fiber-to-fiber contact. Thus, fiber optic connectors incorporating the ferrule of the present invention continue to provide high quality optical connections with a relatively low level of attenuation and return loss even in instances in which the fiber optic connectors are decoupled and subsequently remated to other fiber optic connectors.